2-aminobenzoazoles as activators for vulcanization of rubber

ABSTRACT

A class of 2-aminobenzoazoles is described which is used with primary accelerators to enhance the vulcanization rate of rubber. The new vulcanization activators are characterized by the formula   IN WHICH Y is oxygen or sulfur, X is hydrogen, alkyl, alkoxy, nitro, halo or hydroxy, and n is one or two; when n is one R is hydrogen, alkyl, aryl, cycloalkyl, aralkyl, hydroxyalkyl, or alkenyl; when n is two R is alkylene. The conjoint use of the new activators with thiazole accelerators is particularly advantageous since the vulcanization rate is increased without affecting the processing safety of the vulcanizable composition.

United States Patent [191 Boustany et a1.

[ June 18, 1974 Z-AMINOBENZOAZOLES AS ACTIVATORS FOR VULCANIZATION OF RUBBER [75] Inventors: Kamel Boustany, Akron, Ohio; John Joseph DAmico, Saint Louis, Mo.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: July 19, 1972 [21] App]. No.: 273,173

[52] US. Cl. 260/79.5 B, 260/784, 260/788 [51] Int. ,Cl C08c 11/52, C08c 9/00, C08f 27/06 [58] Field of Search 260/79,5 B, 784, 788

[56] References Cited UNITED STATES PATENTS 1,546,713 7/1925 Bruni 260/788 2,261,042 10/1941 Williamsm. 260/788 2,863,874 12/1958 Gregory 260/306.8 2,945,834 7/1960 Coutler 260/41.5 3,094,496 6/1963 Walker 260/5 Primary Examiner-Joseph J. Schofer Assistant Examiner-C. A. Henderson, Jr.

[5 7] ABSTRACT A class of 2-aminobenzoazoles is described which is used with primary accelerators to enhance the vulcanization rate of rubber. The new vulcanization activators are characterized by the formula alkylene. The conjoint use of the new activators with thiazole accelerators is particularly advantageous since the vulcanization rate is increased without affecting the processing safety of the vulcanizable composition.

16 Claims, N0 Drawings Z-AMINOBENZOAZOLE SAS ACTIVATORS FOR VULCANIZATION OF RUBBER versely affect the processing safety of the stocksand as 1 a consequence, with certain stocks, prevulcanization inhibitors may haveto, be used toavoid premature vulcanization. The activators of this invention exhibit a valuable combination of properties in that they activate the vulcanization cure rate without diminishing thev processing safety. These and other advantages of the invention will become apparent as the description of the invention proceeds.

SUMMARY QF THE lNVENTlQN According to this, invention the vulcanization rate of vulcanizable rubber compositions containing sulfurvulcanizingagent and thiazole accelerator is enhanced by incorporating therein an effective amount of'a com! pound of the formula n h ch Y is. oxygen or iilfunXfishydrgen. ower aly e a k y 'nitrc. c qr bromo. iodo, fluc o... or hydroxy and n is one or-two; when n is one R is hydro-. gen, alkyl, aryl, cycloalkyl, aralkyl, hydroxyalkyl and alkenyl, when n is two R is alkylene. In a preferred class. of activators X is hydrogen, Y is sulfur, n is one and R is an unsubstituted saturated aliphatic radical.v

Alkyl is the radical derived by removal ofone hydro gen atom from an alkane whichradical has, the fomtula; C,.H The alk-yl radical may be primary, secondary or tertiary and the; alkyl chains; thereof may be branched or unbranched. Alkyl radicals of l'.2 0 .carbon. atoms are suitable with radicals of? l=l0carbon atoms, being preferred. According to this invention loweralkyl means radicals of l'.5 carbon atoms. Cycl'oalkyl radicals of -1 2; carbon atoms are suitable with radicals of 58 carbon atoms, being preferred. Aralkyl is a mono'valent alkyl radical having aphenyl radical attached to a carbon atom ofthe alkyl chain. Aralkyl radicals of 7-10 carbon atoms arepreferred. Aryl is a monovalent radical derived by removal of one hydrogenatomfrom an aromatic hydrocarbon. The aryl radical may be sift stitutedin the aromatic nucleus by lower alkylgroups. Aryl radicals of 6-.l 2 carbon atoms are; suitable. Phenyl is the preferred aryl radical but-radicals of the naphtha, lene series are suitable. Hydroxyalkyl isa-radical-derived by removal ofa hydrogen atom from a carbon atom of an aliphatic alcoholfl'he'alkyl radical isthe same as. above except one hydrogen atom isreplaced by hydroxy. Alkenyl is the radical derivedby removal of onehydrogen atom from'an alkene-whichradical has the fonnula C,,H Alkenyl radicals of l-8 carbon atoms are preferred. Alkylene means a divalent alkyl radical wherein each valence is attached to an acyclic or cyclic aliphatic carbon atom. Alkylene radicals of 1-8 carbon atoms are preferred. The alkylene chain may be interrupted by a phenylene radical.

Examples of R are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl, hexyl, octyl, decyl, dodecyl, cetyl, eicosyl, cyclopentyLcyclohexyl, cyclooctyl, cyclodecyl, cyclododecyl, benzyl, alphamethyl benzyl, alpha,alpha-dimethyl benzyl, phenethyl, xylyl, phenyl, naphthyl, tolyl, 4-ethyl phenyl, ethyltolyl, propylphenyl, butylphenyl, hexylphenyl, hydroxymethyl, 2-hydroxyethyl, 2-hydroxypropyl, 3- hydroxypropyl, vinyl, allyl, butenyl, methylene, dimethylene, trimethylene, l-methyl-dimethylene, tetramethylene, pentamethylene, hexamethylene,. heptamethylene, octamethylene, l,4-dimethyltetramethylene, xylylene and cyclohexylene.

illustrative examples of suitable activators of the invention are 2-aminobenzothiazole, 2-( N- methylamino)benzothiazole, 2-( N-isopropylamino benzothiazole, 2-(N-tert-butylamino)benzothiazole,

ylamino)benzothiazole, 2-(N-cyclohexylamino)benzothiazole, 2-(anilino)benzothiazole, 2-( N-benzylamino)benzothiazole, 2-(N- tolylamino)benzothiazole, 2-( N-3-hydroxyptopylamino)benzothiazole, 2-(-N- allylamino)benzothiazole, N,N-bis(Z-benzothiazolyl- )ethylenediamine and similar 2-aminobenzoxazoles.

Further examples of suitable 2-aminoazoles are described in the following references which are incorporated herein by reference: .1. Chem. Soc, 1561 (1958),. J, Chem. 500., 3311.1 (1949-), J. Chem. 500., 2951. (1926), and]. Pharm. Sci., 53, 538 (1964). The improved. compositions of the invention comprise die-ne rubber, sulfur-vulcanizing agent, thiazole. accelerator and an amount effective to enhance the vulcanization rate of the composition of a 2- aminoazole of this invention. Of coursc,.the composition maycontain additional components which are normally elements of vulcanizable compositions. The 2- aminoazoles are incorporated into the composition by milling or mixing inzaccordance. with conventional procedures. The; compositions are then heated to effect vulcanization. The temperature and time at which the compositions are cured varies depending upon the. amounts and type of components in the'vulcanizable composition. Generally, the temperature is between l450F and the time is between a few minutes to an-houror more. At all cure conditions normally encountered, the activators of the-invention enhanced the vulcanization rate.

The activators of the invention can be used in natural and synthetic rubbers andmixtures thereof; Any diene rubber having sufiicientunsaturation to be sulfur vul- 3 synthetic polybutadiene, particularly cis-polyisoprene and cis-polybutadiene. I I For the purposes of this invention, sulfur-vulcanizing' agent means elemental sulfur or sulfur-containingvul 4 1 time (t inriiinutes required for the Mooney reading to rise five points above the minimum viscosity is recorded. Longer times on the Mooney Scorch test are indicative of-gr'eater processing safety. The cure charcanizing agent, for example, an amine disulfide or a 5 acteristics of the'stocks are determined by a Monsanto polymeric polysulfide. The various types of sulfur- Oscillating Disk Rheometer at the 1nd1cated temperacontaining vulcanizing agents are known to those ture. Th tim to) 111 nut r q red f r a se f tw killed i h art f bb vulcanizatiom Rheometer units above the m1n1mum readmg and the The primary accelerators may comprise any of the ('90) q m Ohm!" 90% f the Rheometer thiazole vulcanization accelerators and mixtures maximum l are recorded- The (hfferehce (91712) {hereof known [0 the ar'[ Suitable thiazole accelerators is indicative Of tht} cure rate Of the stock. Small Values are 2-mercaptobenzothiazole, bis(2-benzothiazolyl)dif '90-' 2 Indicate fllslef Cure tlmei VUICimKZlWS are sulfide, and 2-benzothiazolesulfenamides and thiosulp p y Press h g the 5I0Ck5 at indicated fenamides. The sulfenamides may be represented by temperature for the Tequlred to achleve ophmum the f l l5 cure as determined from Rheometer data and the physical properties of the vulcanizates are measured and re- R1 corded. The following styrene-butadiene rubber masterbatch is prepared to illustrate the properties of the activators of this invention. All parts are by we1ght. in which T is 2-benzothiazolyl or substituted-2- benzothiazolyl, .r is one or two, R, and R of l-20 carbon atoms are independently alkyl, benzyl, phenyl or 3BR Masterbatch cycloalkyl and one may be hydrogen, or R, and R may be alkylene which along with the nitrogen atom to which they are attached form a heterocyclic radical. I v The alkylene radical maybe interrupted by another Oil-extendedSIyrenE-bumdienerubber 137-5 hetero-atom such as O, S, or NH-. The g 'gg z gz 18 amount of primary accelerator is generally between farnacecarbon black 65.0 0.2-2.0 parts per 100 parts rubber with 0.5-1.5 parts Hydmcarbc" Softener TOTAL 208.0 being preferred.

The amount of activator for the practice of the invention depends upon other components in the vulcaniz- Vulcanizable compositions are prepared by mixing able COmPOSIIIOH. Generally. Small amounts are suffisulfur, accelerator and activator with portions of the cient to enhance the vulcanization rate. Usually the masterbatch. To some stocks, an antidegradant or quantity is between 0.1 to 4.0 parts per 100 parts rubscorch inhibitor or both are added. The properties of ber with about l-2 parts being preferred, however. the stocks are determined as previously described and even larger amounts may be used if desired. are shown in Tables l-Vl.

' TABLE 1 Stock 1 2 3 4 5 6 SBR Masterbatch 208 v Sulfur 2.0 N- l ,3-dimethylbutyl-N'-phenyl- 2.0 p-phenylenecliamine N-(Cyclohexylthio)phthalimide 0.2 N-tert-butyl-Z-benzothiazolel .0 sulfenamide Z-aminobenzothiazole 0.2 0.4 0.8 L6 2.0

Mooney Data at 135C I 1,. minutes 27.9 27.5 28.8 30.4 28.5 27.9

Rheometer Data at 153C 1,, minutes 9.5 9.0 9.5 9.5 9.5 9.5 1.... minutes 28.5 27.0 27.5 26.5 24.5 235 1, 4, 19.0 18.0 18.5 17.0 15.0 14.0

Stress-Strain Data at l53C Cure time. minutes 45 45 45 40 40 300% modulus,-psi 1250 1210 l360 1310 1200 1240 uh. tensile. psi 2590 3150 3050 3200 2920 3020 Ult. Elongation, '71 490 550 530 550 540 550 PREFERRED EMBODIMENTS The following tables illustrate the improved vulcanization rates obtained by incorporating the activators into rubber. For all the rubber stocks tested. as illustrative of the invention. Mooney scorch time at l3'5C is determined by means of a Mooney plastometer. The

The data of Table I show the results of a concentration study using 2-aminobenzothiazole as activator. The results indicate that the processing safety of the stocks isessentially unaffected, even at'high concentratio'ns', bythe activator. The Rheometer data show that the time required to obtain of maximum torque decreases with increasing amounts of activator. For exactivator is five minutes less than the control. The

erator the activator enhances the vulcanization rate as shown by the Rheometer data and cure times without affecting the processing safety. The data of Table 111 i1- lustrate the effectiveness of 2-aminobenzothiazo1e to stress-strain data further illustrate the shorter times reactivate the cure of stocks containing scorch inhibitors. quired to cure stocks containing the activator. The results indicate that the processing safety of the The activity of 2-aminobenzothiazo1e as an activator stocks may be substantially increased with inhibitors is further illustrated with five different primary accelerand that the cure times may be maintained by use of the ators in Table 11. The results show that with each accelinstant activators.

TABLE 11 Stock No. 1 z 3 4 5 6 7 s u 10 SBR Mastcrbatch 208 Sulfur 2 2.5 2.5 N-1.3-dimcthy1huty1-N-phcny1-p-phcny1cnc- 2 diaminc 2-( 2.t'i-Dimcthyl-morpholinothio)bcnzothiazolc 1.0 1.0 N.N-Diisopropy1-2-hcnzothiazolcsulfcnumidc 1.0 1 0 Z(Mnrpholinothio)hcnzothiazolc 1 0 1.0 2-( Morpholinodithio )hcnzothiuzolc 1.0 1.0 Bis-( Z-hcnzothiazolyl )disulfidc 1.2 1.2 2-Aminubcnzothiazo1c 1.0 1.0 1.0 1.0 0.8 Mooney data at 135C I minutes 29.8 28.3 32.2 27.0 26.3 26.1 13.4 15.2 12.0 11.4

Rheometer Data at 153C 1,. minutes 10.2 10.0 9.5 9.5 9.5 9.5 6.5 7.0 5.0 5.0 1 minutes 33.2 28.0 37.5 35.5 31.5 25.5 24.0 20.0 39.5 25.0 1 -1, 23.0 18.0 28.0 26.0 22.0 16.0 17.5 13.0 34.5 20.0

Stress-Strain Data at 153C I Cure time. minutes 45 55 55 45 45 35 55 300% Modulus. psi 1250 1290 1300 1350 1260 1360 1200 1200 1480 1560 Ult. Tunsilc Str.. psi 2950 3040 2900 3000 31 10 3150 2600 2820 2690 2700 Ult. Ehmgatinn, 71 520 520 500 520 540 540 510 520 450 430 TABLE 111 Stock No. 1 2 3 5 SBR Mastcrbatch 208 Sulfur 2 N-l,3-dimethylbutyl-N'-pheny1- 2 p-phenylcncdiaminc N-tcrt-butyl-Z-bcnzothiaio1c- 1 sulfenamide Z-Aminobenzothiazole 2.0 1.0 2.0 N-(Cyclohexylthio)phthalimide 0.5 0.5 0.5

Mooney Scorch Data at 135C minutes 22.5 22.9 40.4 40.0 37.4

Rheometer Data at 153C 1,, minutes 11.0 1 1.0 16.5 16.2 16.0 I minutes 29.5 23.0 38.7 33.8 30.5 1 -1 18.5 12 .0 22.2 17.6 14.5

Stress-Strain Data at 153C Cure Time. minutes 50 40 60 50 45 300% Modulus. psi 1290 1340 1280 1250 1350 Ult. Tensile. psi 2940 2800 2800 2890 2900 Ult. Elongation. 71 520 500 500 530 520 TABLE IV Stock No. 1 2 3 4 5 SBR Mas'tcrhatch 20s Sulfur 2 N-tcrt-2-hcnzothiazo1c sulfcnamidc 1 Z-Aminobenzothiazolc 2.0 2-( N-mcthylamino )hcnzothiazolc 2.0 2-(N-propylumino)hcnzoxazolc 2.0 2-(N-hcnzylaminu)hcnzothiazolc 2.0

Mooney Scorch Data at C I minutes 19.3 21.3 111.9 20.1 19.9

Rheometer Data at 153C 1,. minutes 9.3 9.0 8.9 9.2 9.0 In. minutes 27.0 19.7 19.9 19.0 21.0 [ml-I] 17.7 10.7 11.0 9.8 12.0

Ult. Elongation. 24

'IABI lV-Continued Stock No. l

Strcss-truig Dgtu at lS/C Cure Timc. minutes 300% Modulus, psi Ult. Tensile. psi

Stock No.

SBR Masterbatch Sulfur N-l.3-dimethylbutylN'-phcnylp-phenylcncdiaminc N-tert-butyl-2-benzothiazolesulfcnamidc Z-Aminobenzothiazole 2-Anilinobenzothiazole 2-(N-2-hydroxycthylamin0)- benzothiazolc 2-(N-allylamino)bcnzothiazolc Mooney Scorch Data at 135C 1,, minutes Rheometer Data at l53C 1,, minutes 1 minutes ea-"2 Stress-Strain Data at 153C Cure Time. minutes 300% Modulus, psi Ult. tensile. psi Ult. Elongation.

Stock No.

SBR Masterbntch 208 Sulfur N-l .3-dimethylbutyl-N'-phenylp-phcnylcnediaminc N-tcrt-bulyl-2-bcnzothiazolc sult'cnamidc 2-(N mcthylaminol-fi-nitrobenzothiuzolc 2-(N-mcthylamino)bcnzothiazole N.N'-his( Z-hcnzothiazolyl ethylcncdiaminc Mooney Scorch Data at lC I minutes Rheomctcr Data at I53C 1,. minutes I minutes Stress-Strain Data at 153C ure time. minutes 300% Modulus. psi

Ult. Tcnsilc. psi

Ult. Elongation. Z

l0.5 25.0 I4.S

sive property or privilege is claimed are defined as follows:

l. The vulcanizable composition comprising styrenebutadiene rubber, sulfur-vulcanizing agent, thiazole accelerator and an amount effective to enhance the vulcanization rate of the composition of a compound of the formula 9 in which Y is oxygen or sulfur, X is hydrogen, lower alkyl, lower alkoxy, nitro, halo or hydroxy, and n is one or two; when n is one R is hydrogen, alkyl of l-2O carbon atoms, aryl of 6-12 carbon atoms, cycloalkyl of -l 2 carbon atoms, aralkyl of 7-10 carbon atoms, hydroxyalkyl of lcarbon atoms, or alkenyl of l-8 carbon atoms, when n is two R is alkylene of 1-8 carbon atoms.

2. The composition of claim I in which X is hydrogen, Y is sulfur, and n is one.

3. The composition of claim 2 in which R is hydrogen.

4. The composition of claim 2 in which R is lower alkyl.

5. The composition of claim 2 in which R is methyl.

6. The composition of claim 2 in which R is allyl. 7. The composition of claim 2 in which R is benzyl.

8. The composition of claim 2 in which the sulfurvulcanizing agent is sulfur and the accelerator is 2-benzothiazolesulfenamide.

9. The process for vulcanizing styrene-butadiene rubber compositions containing sulfur-vulcanizing agent and thiazole accelerator which comprises incorporating into the composition an amount effective to enhance the vulcanization rate of the composition of the compound of the formula x t/ C-NH- in which Y is oxygen or sulfur, X is hydrogen, lower alkyl, lower alkoxy, nitro, halo, or hydroxy, and n is one or two; when n is one R is hydrogen, alkyl of 1-20 carbon atoms, aryl of 6-12 carbon atoms, cycloalkyl of 5-12 carbon atoms, aralkyl of 7-10 carbon atoms, hydroxyalkyl of l-20 carbon atoms, or alkenyl of l-8 carbon atoms, when n is two R is alkylene of l-8 carbon atoms and heating to effect vulcanization.

10. The process of claim 9 in which X is hydrogen, Y is sulfur, and n is one.

11. The process of claim 9 in which R is hydrogen.

12. The process of claim 9 in which R is lower alkyl.

13. The process of claim 9 in which R is methyl.

14. The process of claim 9 in which R is allyl.

15. The process of claim 9 in which R is benzyl.

16. The process of claim 9 in which the sulfurvulcanizing agent is sulfur and the accelerator is a 2-benzothiazolesulfenamide.

I i The composition of claim 2 in which R is 2- hydroxyethyl.

18. The process of claim 9 in which R is Z-hydroxyethyl. 

2. The composition of claim 1 in which X is hydrogen, Y is sulfur, and n is one.
 3. The composition of claim 2 in which R is hydrogen.
 4. The composition of claim 2 in which R is lower alkyl.
 5. The composition of claim 2 in which R is methyl.
 6. The composition of claim 2 in which R is allyl.
 7. The composition of claim 2 in which R is benzyl.
 8. The composition of claim 2 in which the sulfur-vulcanizing agent is sulfur and the accelerator is 2-benzothiazolesulfenamide.
 9. The process for vulcanizing styrene-butadiene rubber compositions containing sulfur-vulcanizing agent and thiazole accelerator which comprises incorporating into the composition an amount effective to enhance the vulcanization rate of the composition of the compound of the formula
 10. The process of claim 9 in which X is hydrogen, Y is sulfur, and n is one.
 11. The process of claim 9 in which R is hydrogen.
 12. The process of claim 9 in which R is lower alkyl.
 13. The process of claim 9 in which R is methyl.
 14. The process of claim 9 in which R is allyl.
 15. The process of claim 9 in which R is benzyl.
 16. The process of claim 9 in which the sulfur-vulcanizing agent is sulfur and the accelerator is a 2-benzothiazolesulfenamide.
 17. The composition of claim 2 in which R is 2-hydroxyethyl.
 18. The process of claim 9 in which R is 2-hydroxyethyl. 